The Radiation Core will provide the irradiation facilities in support of all of the projects in the program. This core is housed Richardson Laboratories of the Department of Radiation Oncology and currently consists of three irradiators, a J.L. Shepherd Mark I, Model 30, Cesium Irradiator, a J.L. Shepherd Mark I, Model 68A, Cesium Irradiator and a Philips RT-250 orthovoltage irradiator. The cesium irradiators are specifically designed for experimental gamma-irradiations. They contain 2,200 Ci/137 Cs sources. Tissue culture flasks are irradiated by stacking them on the rotating platform. A special tube holder can accommodate test tubes with volumes up to 50 ml. The cesium irradiators are suitable for the majority of the irradiations required by this program; however, orthovoltage machine serves as both a back-up for the cesium sources and as a sources for irradiation at variable energies. Dr. Bengt Bjarngard is Director of the Radiation Core. His responsibilities include training personnel in the proper and safe use of the instruments and ensuring compliance with NRC regulations. Dr. Bjarngard chairs an Internal Advisory Committee. The Committee meets as needed to set rules and policies for instrument use and to make decisions concerning maintenance and repairs. The Committee guarantees fair and equitable use of the instruments among the investigators.